Flexible display device with space reducing wire configuration

ABSTRACT

There is provided a flexible display having a plurality of innovations configured to allow bending of a portion or portions to reduce apparent border size and/or utilize the side surface of an assembled flexible display.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/556,087 filed on Nov. 28, 2014, which is incorporated by referenceherein in its entirety.

BACKGROUND

Technical Field

This relates generally to electronic devices, and more particularly, toelectronic devices with a display.

Description of the Related Art

Electronic devices often include displays. For example, cellulartelephones and portable computers include displays for presentinginformation to a user. Components for the electronic device, includingbut not limited to a display, may be mounted in a plastic or a metalhousing.

An assembled display may include a display panel and a number ofcomponents for providing a variety of functionalities. For instance, oneor more display driving circuits for controlling the display panel maybe included in a display assembly. Examples of the driving circuitsinclude gate drivers, emission (source) drivers, power (VDD) routing,electrostatic discharge (ESD) circuits, multiplex (mux) circuits, datasignal lines, cathode contacts, and other functional elements. There maybe a number of peripheral circuits included in the display assembly forproviding various kinds of extra functions, such as touch sense orfingerprint identification functionalities. Some of the components maybe disposed on the display panel itself, often in the periphery areasnext to the display area, which is referred in the present disclosure asthe non-display area and/or the inactive area.

Size and weight are of the critical importance in designing modernelectronic devices. Also, a high ratio of the active area size comparedto that of inactive area, which is sometimes referred to as the screento bezel ratio, is one of the most desired feature. However, placingsome of the aforementioned components in a display assembly may requirelarge inactive area, which may add up to a significant portion of thedisplay panel. Large inactive area tends to make the display panelbulky, making it difficult to incorporate it into the housing ofelectronic devices. Large inactive area may also necessitate a largemasking (e.g., bezel, borders, covering material) to cover a significantportion of the display panel, leading to unappealing device aesthetics.

Some of the components can be placed on a separate flexible printedcircuit (FPC) and positioned on the rear side of the display panel. Evenwith such a configuration, however, the interfaces for connecting theFPC and the wires between the active area and the connection interfacestill limit how much reduction in the size of the inactive area can berealized by placing components on a separate FPC.

BRIEF SUMMARY

Accordingly, it is desirable to bend the base substrate where thedisplay area and the inactive area are formed thereon. This would alloweven some of the inactive area to be positioned behind the active areaof the display panel, thereby reducing or eliminating the inactive areathat needs to be hidden under the masking or the device housing. Notonly does the bending of the base substrate will minimize the inactivearea size need to be hidden from view, but it will also open possibilityto various new display device designs.

However, there are various new challenges that need to be solved inproviding such flexible displays. The components formed directly on thebase substrate along with the display pixels tend to have tremendouslysmall dimensions with unforgiving margin of errors. Further, thesecomponents need to be formed on extremely thin sheet to provideflexibility, making those components extremely fragile to variousmechanical and environmental stresses instigated during the manufactureand/or in the use of the displays. If care is not taken, the mechanicalstresses from bending of the flexible display can negatively affect thereliability or even result in complete component failure. Even amicro-scale defect in the component thereof can have devastating effectson the performance and/or reliability of the display pixels amounting toscrap the entire display panel without an option to repair. On the otherhand, simply increasing the bending radius to ease the bend stress maymake it difficult to garner any significant benefits in bending the basesubstrate of the display panel.

As such, various factors and special parameters must be taken inconsideration in designing a flexible display. An aspect of the presentdisclosure is related to a flexible display, which includesconfigurations for wire traces to withstand bend stress for reliableoperation of the flexible display.

In an aspect, a flexible display having an array of pixels is provided.The flexible display includes a flexible base layer defined with adisplay area and a non-display area. The plurality of pixels, which mayinclude one or more organic light-emitting diodes, is provided in thedisplay area of the flexible base layer. The flexible display furtherincludes a first wire trace and a second wire trace positioned adjacentto each other on the flexible base layer. The first wire trace includesa trace of a conductive line, which is covered with at least oneinsulation layer that is patterned according to the trace of theconductive line. The second wire trace also includes a trace of aconductive line and one or more of insulation layers patterned accordingto the trace of the conductive line. Space is provided between the firstwire trace and the second wire trace. In this space, at least one of theinsulation layers patterned according to the trace of the conductivelines of the first and second wire traces is absent.

In some embodiments, both the first wire trace and the second wire tracehave a trace design in which one or more of a non-linear sections isprovided in the wire trace. The non-linear section has a convex side anda concave side, and the convex side of the non-linear section in one ofthe first and second wire traces is positioned next to the concave sideof the non-linear section in the other wire trace.

In some embodiments, the trace design of the first wire trace and thetrace design of the second wire trace may differ from each other, andthe non-linear section in one of the first and second wire traces may belarger than the non-linear section in the other wire trace.

In another aspect, a flexible display apparatus includes a flexible baselayer that has a display area and a non-display area. An array ofpixels, which includes one or more organic light-emitting diodes, isprovided on the display area of the flexible base layer. The flexibledisplay apparatus further includes a first wire trace and a second wiretrace on the flexible base layer. Both the first wire trace and thesecond wire trace have a trace design, in which each wire trace isprovided with an indented section between two distended sections of therespective wire trace. The first wire trace and the second wire traceare arranged in a staggered configuration such that one of the distendedsections of the first wire trace is aligned next to the indented sectionof second wire trace.

In some embodiments, a channel of space is provided between the firstwire trace and the second wire trace, and one or more insulation layersprovided under and over the first wire trace and the second wire traceare absent in the channel of space between the first and second wiretraces.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the embodiments discussed herein. A furtherunderstanding of the nature and advantages of certain embodiments may berealized by reference to the remaining portions of the specification andthe drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematic view of an exemplary flexible displayapparatus according to embodiments of the present disclosure.

FIG. 2 illustrates exemplary arrangement of a substantially flat portionand bend portion of a flexible display apparatus according toembodiments of the present disclosure.

FIGS. 3A-3B illustrate exemplary arrangement of active areas of aflexible display apparatus according to embodiments of the presentdisclosure.

FIG. 4 illustrates simplified stack up structure of components in anexemplary flexible display apparatus according to embodiment of thepresent disclosure.

FIG. 5 illustrates various examples of bend patterns applicable tofacilitate bending of a display apparatus.

FIGS. 6A-6C are cross-sectional views of illustrative arrangement ofcomponents in a flexible display apparatus according to variousembodiments of the present disclosure.

FIGS. 7A-7B illustrate schematic view of an exemplary multi-layeredconductive lines and insulation layers according to embodiments of thepresent disclosure.

FIG. 8 illustrates schematic view of exemplary non-split strain-reducingtrace designs usable for wire traces in a flexible display apparatusaccording to embodiments of the present disclosure.

FIGS. 9A-9B illustrate a schematic view of exemplary strain-reducingwire trace designs having a plurality of sub-traces that split and mergeat a certain interval according to embodiments of the presentdisclosure.

FIG. 10 illustrates an exemplary arrangement of the wire tracesincluding indented sections and distended sections.

FIGS. 11A-11B illustrate schematic cross-sectional views of exemplarytrace designs usable for wire traces in a flexible display apparatusaccording to embodiments of the present disclosure.

FIGS. 12A-12B illustrate schematic views of an exemplary strain-reducingwire trace design with modified portions adopted for the wire trace toextend across the areas with different plane levels within the flexibledisplay according to embodiments of the present disclosure.

FIG. 13A illustrates a schematic view of an exemplary configuration forthe crack stopper structures according to an embodiment of the presentdisclosure.

FIGS. 13B-13C illustrate schematic views of exemplary configurationsnear the notched area of the flexible display apparatus.

FIGS. 14A-14C illustrate schematic views of the flexible displayprovided with a micro-coating layer according to embodiments of thepresent disclosure.

FIGS. 15A-15B illustrate schematic views of embodiments of the flexibledisplay in a bent state, which are provided with a micro-coating layeraccording to embodiments of the present disclosure.

FIG. 16 illustrates a schematic view of an exemplary strain-reducingwire trace design provided with elongated channel(s) for improvingspread dynamics of a micro-coating layer.

DETAILED DESCRIPTION

Flexible Display

FIG. 1 illustrate exemplary flexible display 100 which may beincorporated in electronic devices. Referring to FIG. 1, the flexibledisplay 100 includes at least one active area (i.e., display area), inwhich an array of display pixels are formed therein. One or moreinactive areas may be provided at the periphery of the active area. Thatis, the inactive area may be adjacent to one or more sides of the activearea. In FIG. 1, the inactive area surrounds a rectangular shape activearea. However, it should be appreciated that the shapes of the activearea and the arrangement of the inactive area adjacent to the activearea are not particularly limited as the exemplary flexible display 100illustrated in FIG. 1. The active area and the inactive area may be inany shape suitable to the design of the electronic device employing theflexible display 100. Non-limiting examples of the active area shapes inthe flexible display 100 include a pentagonal shape, a hexagonal shape,a circular shape, an oval shape, and more.

Each pixel in the active area may be associated with a pixel circuit,which includes at least one switching thin-film transistor (TFT) and atleast one driving TFT on the backplane of the flexible display 100. Eachpixel circuit may be electrically connected to a gate line and a dataline to communicate with one or more driving circuits, such as a gatedriver and a data driver positioned in the inactive area of the flexibledisplay 100.

For example, one or more driving circuits may be implemented with TFTsfabricated in the inactive area as depicted in FIG. 1. Such a drivingcircuit may be referred to as a gate-in-panel (GIP). Also, some of thecomponents, such as data drive-IC, may be mounted on a separate printedcircuit and coupled to a connection interface (Pads/Bumps) disposed inthe inactive area using a printed circuit film such as flexible printedcircuit board (FPCB), chip-on-film (COF), tape-carrier-package (TCP) orany other suitable technologies. As will be described in further detailbelow, the inactive area with the connection interface can be bent awayfrom the plane of the adjacent portion of the flexible display so thatthe printed circuit film (e.g., COF, FPCB and the like) is positioned atthe rear side of the flexible display 100.

The flexible display 100 may include various additional components forgenerating a variety of signals or otherwise operating the pixels in theactive area. Non limiting examples of the components for operating thepixels include an inverter circuit, a multiplexer, an electro staticdischarge (ESD) circuit and the like. The flexible display 100 may alsoinclude components associated with functionalities other than foroperating the pixels of the flexible display 100. For instance, theflexible display 100 may include components for providing a touchsensing functionality, a user authentication functionality (e.g., fingerprint scan), a multi-level pressure sensing functionality, a tactilefeedback functionality and/or various other functionalities for theelectronic device employing the flexible display 100. Some of theaforementioned components can be placed in the inactive area of theflexible display 100 and/or on a separate printed circuit that isconnected to the connection interface of the flexible display 100.

Flat/Bend Portions

Multiple parts of the flexible display 100 can be bent along the bendline BL. The bend line BL in the flexible display 100 may extendhorizontally (e.g., X-axis shown in FIG. 1), vertically (e.g., Y-axisshown in FIG. 1) or even diagonally. Accordingly, the flexible display100 can be bent in any combination of horizontal, vertical and/ordiagonal directions based on the desired design of the flexible display100.

As mentioned, one or more edges of the flexible display 100 can be bentaway from the plane of the central portion along the bend line BL.Although the bend line BL is depicted as being located near the edges ofthe flexible display 100, it should be noted that the bend lines BL canextend across the central portion or extend diagonally at one or morecorners of the flexible display 100. Such configurations would allow theflexible display 100 to provide a foldable display or a double-sideddisplay having display pixels on both outer sides of a folded display.

With the ability to bend one or more portions of the flexible display100, part of the flexible display 100 may be defined as a substantiallyflat portion and a bend portion. A part of the flexible display 100 mayremain substantially flat and referred to as a substantially flatportion of the flexible display 100. A part of the flexible display 100may be bent in a certain bend angle from the plane of an adjacentportion, and such portion is referred to as a bend portion of theflexible display 100. The bend portion includes a bend allowancesection, which can be actively curved in a certain bend radius.

It should be understood that the term “substantially flat” includes aportion that may not be perfectly flat. For example, the concave centralportion and the convex central portion depicted in FIG. 2 may bedescribed as a substantially flat portion in some embodiments discussedin the present disclosure. In FIG. 2, one or more bend portions existnext to the convex or concave central portion, and bent inwardly oroutwardly along the bend line in a bend angle about a bend axis. Thebend radius of the bend portion is smaller than the bend radius of thecentral portion. In other words, the term “substantially flat portion”refers to a portion with a lesser curvature than that of an adjacentbend allowance section of the flexible display 100.

Depending on the location of the bend line BL in the flexible display100, a portion on one side of the bend line may be positioned toward thecenter of the flexible display 100, whereas the portion on the oppositeside of the bend line BL is positioned toward an edge portion of theflexible display 100. The portion toward the center may be referred toas the central portion and the portion toward the edge may be referredto as the edge portion of the flexible display 100. Although this maynot always be the case, a central portion of the flexible display 100can be the substantially flat portion and the edge portion can be thebend portion of the flexible display 100. It should be noted that asubstantially flat portion can also be provided in the edge portion ofthe flexible display 100. Further, in some configuration of the flexibledisplay 100, a bend allowance section may be positioned between twosubstantially flat portions.

As mentioned above, bending the inactive area allows to minimize or toeliminate the inactive area to be seen from the front side of theassembled flexible display 100. Part of the inactive area that remainsvisible from the front side can be covered with a bezel. The bezel maybe formed, for example, from a stand-alone bezel structure that ismounted to the cover layer 114, a housing or other suitable componentsof the flexible display 100. The inactive area remaining visible fromthe front side may also be hidden under an opaque masking layer, such asblack ink (e.g., a polymer filled with carbon black) or a layer ofopaque metal. Such an opaque masking layer may be provided on a portionof various layers included in the flexible display 100, such as a touchsensor layer, a polarization layer, a cover layer, and other suitablelayers.

Active Areas

In some embodiments, the bend portion of the flexible display 100 mayinclude an active area capable of displaying image from the bendportion, which is referred herein after as the secondary active area.That is, the bend line BL can be positioned in the active area so thatat least some display pixels of the active area is included in the bendportion of the flexible display 100.

FIGS. 3A and 3B each illustrates an exemplary configuration of activeareas in an embodiment of flexible display 100 of the presentdisclosure. In the configuration depicted in FIG. 3A, the matrix ofpixels in the secondary active area of the bend portion may becontinuously extended from the matrix of the pixels in the active areaof the central portion. Alternatively, in the configuration depicted inFIG. 3B, the secondary active area within the bend portion and theactive area within the central portion of the flexible display 100 maybe separated apart from each other by the bend allowance section of theflexible display 100. Some components in the central portion and thebend portion can be electrically connected via one or more conductiveline 120 laid across the bend allowance section of the flexible display100.

The pixels in the secondary active area and the pixels in the centralactive area may be addressed by the driving circuits (e.g., gate driver,data driver, etc.) as if they are in a single matrix. In this case, thepixels of the central active area and the pixels of the secondary activearea may be operated by the same set of driving circuits. By way ofexample, the Nth row pixels of the central active area and the Nth rowpixels of the secondary active area may be configured to receive thegate signal from the same gate driver. As shown in FIG. 3B, the part ofthe gate line crossing over the bend allowance section (i.e., bendallowance region) or a bridge for connecting the gate lines of the twoactive areas may have a strain-reducing trace design, which will bedescribed in further detail below.

Depending on the functionality of the secondary active area, the pixelsof the secondary active area can be driven discretely from the pixels inthe central active area. That is, the pixels of the secondary activearea may be recognized by the display driving circuits as being anindependent matrix of pixels separate from the matrix of pixels of thecentral active area. In such cases, the pixels of the secondary activearea may receive signals from at least one discrete driving circuitother than a driving circuit for providing signals to the pixels of thecentral active area.

Regardless of the configuration, the secondary active area in the bendportion may serve as a secondary display area in the flexible display100. Also, the size of the secondary active area is not particularlylimited. The size of the secondary active area may depend on itsfunctionality within the electronic device. For instance, the secondaryactive area may be used to provide images and/or texts such a graphicaluser interface, buttons, text messages, and the like. In some cases, thesecondary active area may be used to provide light of various colors forvarious purposes (e.g., status indication light), and thus, the size ofthe secondary active area need not be as large as the active area in thecentral portion of the flexible display 100.

Stack-Up Structure

FIG. 4 is a simplified cross-sectional view showing an exemplary stackup structure of a flexible display 100 in an embodiment of the presentdisclosure. For convenience of explanation, the central portion of theflexible display 100 is illustrated as being substantially flat, and thebend portions are provided at the edges of the flexible display 100 inFIG. 4.

As shown, one or more bend portions may be bent away from the plane ofthe substantially flat portion in a certain bend angle θ and with a bendradius R about the bending axis. The size of each bend portion that isbent away from the central portion needs not be the same. That is, thelength of the base layer 106 from the bend line BL to the outer edge ofthe base layer 106 at each bend portion can be different from other bendportions. Also, the bend angle θ around the bend axis and the bendradius R from the bend axis can vary between the bend portions.

In the example shown in FIG. 4, the right side bend portion has the bendangle θ of 90°, and the bend portion includes a substantially flatsection. A bend portion can be bent at a larger bend angle θ, such thatat least some part of the bend portion comes underneath the plane of thecentral portion of the flexible display 100 as the bend portion on theleft side of the flexible display 100. Also, a bend portion can be bentat a bend angle θ that is less than 90°.

In some embodiments, the radius of curvatures (i.e., bend radius) forthe bend portions in the flexible display 100 may be between about 0.1mm to about 10 mm, more preferably between about 0.1 mm to about 5 mm,more preferably between about 0.1 mm to about 1 mm, more preferablybetween about 0.1 mm to about 0.5 mm. In some embodiments, the bendradius at a bend portion of the flexible display 100 may be less than0.5 mm.

One or more support layers 108 may be provided at the underside of thebase layer 106 to increase rigidity and/or ruggedness at the selectiveportion of the flexible display 100. For instance, the support layer 108can be provided on the inner surface of the base layer 106 at thesubstantially flat portions of the flexible display 100. The supportlayer 106 may not be provided in the bend allowance section where moreflexibility is needed. The support layer 106 may also be provided on thebase layer 106 of the bend portion that is positioned under the centralportion of the flexible display 100. Increased rigidity at selectiveparts of the flexible display 100 may help in ensuring accurateconfiguration and placement of various components during manufacturingand using the flexible display 100. The support layer 108 can also serveto suppress generation of cracks in the base layer 106, if the baselayer 106 has a higher modulus than the support layer 108.

The base layer 106 and the support layer 108 may each be made of a thinplastic film formed from polyimide, polyethylene naphthalate (PEN),polyethylene terephthalate (PET), other suitable polymers, a combinationof these polymers, etc. Other suitable materials that may be used toform the base layer 106 and the support layer 108 include, a thin glass,a metal foil covered with a dielectric material, a multi-layered polymerstack and a polymer composite film comprising a polymer materialcombined with nanoparticles or micro-particles dispersed therein, etc.Support layers 108 provided in various parts of the flexible display 100need not be made of the same material. For example, a thin-glass layermay be used as a support layer 108 for the central portion of theflexible display 100 while a thin plastic film layer is used as asupport layer 108 for edge portions.

In addition to the constituent material, the thickness of the base layer106 and the support layer 108 is another factor to consider in designingthe flexible display 100. On the one hand, bending of the base layer 106at a small bend radius can be difficult if the base layer 106 hasexcessively high thickness. Also, excessive thickness of the base layer106 can increase mechanical stress to the components disposed thereonduring bending the base layer 106. On the other hand, however, the baselayer 106 can be too fragile to serve as a substrate for variouscomponents of the flexible display if it is too thin.

To meet such requirements, the base layer 106 may have a thickness in arange of about from 5 μm to about 50 μm, more preferably in a range ofabout 5 μm to about 30 μm, and more preferably in a range of about 5 μmto about 16 μm. The support layer 108 may have a thickness from about100 μm to about 125 μm, from about 50 μm to about 150 μm, from about 75μm to 200 μm, less than 150 μm, or more than 100 μm.

In one suitable exemplary configuration, a layer of polyimide with athickness of about 10 μm to about 16 μm serves as the base layer 106while a polyethylene terephthalate (PET) layer with a thickness of about50 μm to about 125 μm serves as the support layer 108. In anothersuitable exemplary configuration, a layer of polyimide with a thicknessof about 10 μm to about 16 μm serves as the base layer 106 while athin-glass layer with a thickness of about 50 μm to about 200 μm is usedas the support layer 108. In yet another suitable exemplaryconfiguration, a thin glass layer is used as the base layer 106 with alayer of polyimide serving as the support layer 108 to suppress breakingof the base layer 106.

During manufacturing, some part of the flexible display 100 may beexposed to external light. Some materials used in fabricating thecomponents on the base layer 106 or the components themselves mayundergo undesirable state changes (e.g., threshold voltage shift in theTFTs) due to the light exposure during the manufacturing of the flexibledisplay 100. Some parts of the flexible display 100 may be more heavilyexposed to the external light than others, and this can lead to adisplay non-uniformity (e.g., mura, shadow defects, etc.). To minimizesuch problems, the base layer 106 and/or the support layer 108 mayinclude one or more materials capable of reducing the amount of externallight passing through in some embodiments of the flexible display 100.

The light blocking material, for instance chloride modified carbonblack, may be mixed in the constituent material of the base layer 106(e.g., polyimide or other polymers). In this way, the base layer 106 mayformed of polyimide with a shade to provide a light blockingfunctionality. Such a shaded base layer 106 can also improve thevisibility of the image content displayed on the flexible display 100 byreducing the reflection of the external light coming in from the frontside of the flexible display 100.

Instead of the base layer 106, the support layer 108 may include a lightblocking material to reduce the amount of light coming in from the rearside (i.e., the support layer 108 attached side) of the flexible display100. The constituent material of the support layer 108 may be mixed withone or more light blocking materials in the similar fashion as describedabove with the base layer 106. Further, both the base layer 106 and thesupport layer 108 can include one or more light blocking materials.Here, the light blocking materials used in the base layer 106 and thesupport layer 108 need not be the same.

While making the base layer 106 and the support layer 108 to block theunwanted external light may improve display uniformity and reducereflection as described above, recognizing alignment marks for accuratepositioning of the components or for carrying out manufacturing processmay become difficult. For example, accurate positioning of thecomponents on the base layer 106 or the alignment during bending of theflexible display 100 can be difficult as the positioning of the layersmay need to be determined by comparing the outer edges of theoverlapping portions of the layer(s). Further, checking for unwanteddebris or other foreign materials in the flexible display 100 can beproblematic if the base layer 106 and/or the support layer 108 blocksthe excessive range(s) of light spectrum (i.e., wavelengths in thevisible, the ultraviolet and the infrared spectrum).

Accordingly, in some embodiments, the light blocking material, which maybe included in the base layer 106 and/or the support layer 108 isconfigured to pass the light of certain polarization and/or the lightwithin specific wavelength ranges usable in one or more manufacturingand/or testing processes of the flexible display 100. By way of example,the support layer 108 may pass the light to be used in quality checkand/or alignment processes (e.g., UV, IR spectrum light) during themanufacturing the flexible display 100, but filter the light in thevisible light wavelength range. The limited range of wavelengths canhelp reduce the display non-uniformity problem, which may be caused bythe shadows generated by the printed circuit film attached to base layer106, especially if the base layer 106 includes the light blockingmaterial as described above.

It should be noted that the base layer 106 and the support layer 108 canwork together in blocking and passing specific types of light. Forinstance, the support layer 108 can change the polarization of light,such that the light will not be passable through the base layer 106.This way, certain type of light can be passed through the support layer108 for various purposes during manufacturing of the flexible display100, but unable to penetrate through the base layer 106 to causeundesired effects to the components disposed on the opposite side of thebase layer 106.

Backplane of the flexible display 100 is implemented on the base layer106. In some embodiments, the backplane of the flexible display 100 canbe implemented with TFTs using low-temperature poly-silicon (LTPS)semiconductor layer as its active layer. In one suitable configuration,the pixel circuit and the driving circuits (e.g., GIP) on the base layer106 are implemented with NMOS LIPS TFTs. In other suitableconfiguration, the backplane of the flexible display 100 can beimplemented with a combination of NMOS LIPS TFTs and PMOS LIPS TFTs. Forinstance, the driving circuit (e.g., GIP) on the base layer 106 mayinclude one or more CMOS circuits to reduce the number of lines forcontrolling the scan signals on the gate line.

Further, in some embodiments, the flexible display 100 may employmultiple kinds of TFTs to implement the driving circuits in the inactivearea and/or the pixel circuits in the active area. That is, acombination of an oxide semiconductor TFT and an LIPS TFT may be used toimplement the backplane of the flexible display 100. In the backplane,the type of TFTs may be selected according to the operating conditionsand/or requirements of the TFTs within the corresponding circuit.

Low-temperature-poly-silicon (LIPS) TFTs generally exhibit excellentcarrier mobility even at a small profile, making them suitable forimplementing condensed driving circuits. The excellent carrier mobilityof the LIPS TFT makes it an ideal for components requiring a fast speedoperation. Despite the aforementioned advantages, initial thresholdvoltages may vary among the LIPS TFTs due to the grain boundary of thepoly-crystallized silicon semiconductor layer.

A TFT employing an oxide material based semiconductor layer, such as anindium-gallium-zinc-oxide (IGZO) semiconductor layer (referredhereinafter as “the oxide TFT”), is different from the LIPS TFT in manyrespects. Despite a lower mobility than the LIPS TFT, the oxide TFT isgenerally more advantageous than the LIPS TFT in terms of powerefficiency. Low leakage current of the oxide TFT during its off stateallows to remain in active state longer. This can be of a greatadvantage for driving the pixels at a reduced frame rate when a highframe rate driving of the pixels is not needed.

By way of example, the flexible display 100 may be provided with afeature in which the pixels of the entire active area or selectiveportion of the active area are driven at a reduced frame rate under aspecific condition. In this setting, the pixels can be refreshed at areduced refresh rate depending on the content displayed from theflexible display 100. Also, part of the active area displaying a stillimage data (e.g., user interface, text) may be refreshed at a lower ratethan other part of the active area displaying rapidly changing imagedata (e.g., movie). The pixels driven at a reduced refresh rate may havean increased blank period, in which the data signal is not provided tothe pixels. This would minimize the power wasted from providing thepixels with the same image data. In such embodiments, some of the TFTsimplementing the pixel circuits and/or the driving circuits of theflexible display 100 can be formed of the oxide TFT to minimize theleakage current during the blank period. By reducing the current leakagefrom the pixel circuits and/or the driving circuits, the pixels canachieve more stable level of luminance even when the display isrefreshed at a reduced rate.

Another feature of the oxide TFT is that it does not suffer from thetransistor-to-transistor initial threshold voltage variation issue asmuch as the LTPS TFTs. Such a property can be of a great advantage whenincreasing the size of the flexible display 100. Threshold shifts underbias stress is also different between LTPS TFT and oxide TFT.

Considering the aforementioned characteristics of LTPS TFT and oxideTFT, some embodiments of the flexible display 100 disclosed herein canemploy a combination of the LIPS TFT and the oxide TFT in a singlebackplane. In particular, some embodiments of the flexible display 100can employ LIPS TFTs to implement the driving circuits (e.g., GIP) inthe inactive area and employ oxide TFTs to implement the pixel circuitsin the active area. Due to the excellent carrier mobility of the LIPSTFTs, driving circuits implemented with LIPS TFTs may operate at afaster speed than the driving circuits implemented with the oxide TFTs.In addition, more condensed driving circuits can be provided with theLIPS TFT, which reduces the size of the inactive area in the flexibledisplay 100. With the excellent voltage holding ratio of the oxide TFTsused in the pixel circuits, leakage from the pixels can be reduced. Thisalso enables to refresh pixels in a selective portion of the active areaor to drive pixels at a reduced frame rate under a predeterminedcondition (e.g., when displaying still images) while minimizing displaydefects caused by the leakage current.

In some embodiments, the driving circuits in the inactive area of theflexible display 100 may be implemented with a combination of N-TypeLIPS TFTs and P-Type LIPS TFTs while the pixel circuits are implementedwith oxide TFTs. For instance, N-Type LIPS TFTs and P-Type LIPS TFTs canbe used to implement a CMOS gate driver (e.g., CMOS GIP, Data Driver)whereas oxide TFTs are employed in at least some part of the pixelcircuits. Unlike the GIP formed entirely of either the P-type or N-typeLIPS TFTs, the gate out signal from the CMOS gate driver can becontrolled by DC signals or logic high/low signals. This allows for morestable control of the gate line during the blank period such that thesuppression of current leakage from the pixel circuit or unintendedactivation of the pixels connected the gate line can be achieved.

It should be noted that a CMOS gate driver or an inverter circuit on thebackplane can be implemented by using a combination of LIPS TFTs andoxide TFTs. For instance, a P-type LIPS TFT and an N-Type oxide TFT canbe used to implement a CMOS circuit. Also, the pixel circuits in theactive area can also be implemented by using both the LIPS TFTs and theoxide TFTs. When employing both kinds of TFTs in the pixel circuitand/or the driving circuit, the LIPS TFT can be strategically placedwithin the circuit to remove bias remaining in a node between oxide TFTsduring their off state and minimize the bias stress (e.g., PBTS, NBTS).In addition, the TFTs in a circuit, which are connected to a storagecapacitor, can be formed of the oxide TFT to minimize leakage therefrom.

The organic light-emitting diode (OLED) element layer 102 is disposed onthe base layer 106. The OLED element layer 102 includes a plurality ofOLED elements, which is controlled by the pixel circuits and the drivingcircuits implemented on the base layer 106 as well as any other drivingcircuits connected to the connection interfaces on the base layer 106.The OLED element layer includes an organic-light emitting materiallayer, which may emit light of certain spectral color (e.g., red, green,blue). In some embodiments, the organic-light emitting material layermay have a stack configuration to emit white light, which is essentiallya combination of multiple colored lights.

The encapsulation 104 is provided to protect the OLED element layer 102from air and moisture. The encapsulation 104 may include multiple layersof materials for reducing permeation of air and moisture to protect OLEDelements thereunder. In some embodiments, the encapsulation 104 may beprovided in a form of a thin film.

The flexible display 100 may also include a polarization layer 110 forcontrolling the display characteristics (e.g., external lightreflection, color accuracy, luminance, etc.) of the flexible display100. Also, the cover layer 114 may be used to protect the flexibledisplay 100.

Electrodes for sensing touch input from a user may be formed on aninterior surface of a cover layer 114 and/or at least one surface of thepolarization layer 110. If desired, an independent layer with the touchsensor electrodes and/or other components associated with sensing oftouch input (referred hereinafter as touch-sensor layer 112) may beprovided in the flexible display 100. The touch sensor electrodes (e.g.,touch driving/sensing electrodes) may be formed from transparentconductive material such as indium tin oxide, carbon based materialslike graphene or carbon nanotube, a conductive polymer, a hybridmaterial made of mixture of various conductive and non-conductivematerials. Also, metal mesh (e.g., aluminum mesh, silver mesh, etc.) canalso be used as the touch sensor electrodes.

The touch sensor layer 112 may include a layer formed of one or moredeformable dielectric materials. One or more electrodes may beinterfaced with or positioned near the touch sensor layer 112, andloaded with one or more signals to facilitate measuring electricalchanges on one or more of the electrodes upon deformation of the touchsensor layer 112. The measurement may be analyzed to assess the amountof pressure at a plurality of discrete levels and/or ranges of levels onthe flexible display 100.

In some embodiments, the touch sensor electrodes can be utilized inidentifying the location of the user inputs as well as assessing thepressure of the user input. Identifying the location of touch input andmeasuring of the pressure of the touch input on the flexible display 100may be achieved by measuring changes in capacitance from the touchsensor electrodes on one side of the touch sensor layer 112. The touchsensor electrodes and/or other electrode may be used to measure a signalindicative of the pressure on the flexible display 100 by the touchinput. Such a signal may be obtained simultaneously with the touchsignal from the touch sensor electrodes or obtained at a differenttiming.

The deformable material included in the touch sensor layer 112 may be anelectro-active material, which the amplitude and/or the frequency of thedeformation is controlled by an electrical signal and/or electricalfield. The examples of such deformable materials include piezo ceramic,electro-active-polymer (EAP) and the like. Accordingly, the touch sensorelectrodes and/or separately provided electrode can activate thedeformable material to bend the flexible display 100 to desireddirections. In addition, such electro-active materials can be activatedto vibrate at desired frequencies, thereby providing tactile and/ortexture feedback on the flexible display 100. It should be appreciatedthat the flexible display 100 may employ a plurality of electro-activematerial layers so that bending and vibration of the flexible display100 can be provided simultaneously or at a different timing. Such acombination can be used in creating sound waves from the flexibledisplay 100.

Components of the flexible display 100 may make it difficult to bend theflexible display 100 along the bend line BL. Some of the elements, suchas the support layer 108, the touch sensor layer 112, the polarizationlayer 110 and the like, may add too much rigidity to the flexibledisplay 100. Also, the thickness of such elements shifts the neutralplane of the flexible display 100 and thus some of the components may besubject to greater bend stresses than other components.

To facilitate easier bending and to enhance the reliability of theflexible display 100, the configuration of components in the bendportion of the flexible display 100 differs from the substantially flatportion of the flexible display 100. Some of the components existing inthe substantially flat portion may not be disposed in the bend portionsof the flexible display 100, or may be provided in a differentthickness. The bend portion may be free of the support layer 108, thepolarization layer 110, the touch sensor layer 114, a color filter layerand/or other components that may hinder bending of the flexible display100. Such components may not be needed in the bend portion if the bendportion is to be hidden from the view or otherwise inaccessible to theusers of the flexible display 100.

Even if the secondary active area is in the bend portion for providinginformation to users, the secondary active area may not require some ofthese components depending on the usage and/or the type of informationprovided by the secondary active area. For example, the polarizationlayer 110 and/or color filter layer may not be needed in the bendportion when the secondary active area is used for simply emittingcolored light, displaying texts or simple graphical user interfaces in acontrast color combination (e.g., black colored texts or icons in whitebackground). Also, the bend portion of the flexible display 100 may befree of the touch sensor layer 114 if such functionality is not neededin the bend portion. If desired, the bend portion may be provided with atouch sensor layer 112 and/or the layer of electro-active material eventhough the secondary active area for displaying information is notprovided in the bend portion.

Since the bend allowance section is most heavily affected by the bendstress, various bend stress-reducing features are applied to thecomponents on the base layer 106 of the bend allowance section. To thisend, some of the elements in the central portion may be absent in atleast some part of the bend portion. The separation between thecomponents in the central portion and the bend portion may be created byselectively removing the elements at the bend allowance section of theflexible display 100 such that the bend allowance section is free of therespective elements.

As depicted in FIG. 4, the support layer 108 in the central portion andthe support layer 108 in the bend portion can be separated from eachother by the absence of the support layer 108 at the bend allowancesection. Instead of using the support layer 108 attached to the baselayer 106, a support member 116 with a rounded end portion can bepositioned underside of the base layer 106 at the bend allowancesection. Various other components, for example the polarization layer110 and the touch sensor layer 114 and more, may also be absent from thebend allowance section of the flexible display 100. The removal of theelements may be done by cutting, wet etching, dry etching, scribing andbreaking, or other suitable material removal methods. Rather thancutting or otherwise removing an element, separate pieces of the elementmay be formed at the selective portions (e.g., substantially flatportion and the bend portion) to keep the bend allowance section free ofsuch element.

Rather than being entirely removed from the bend portion, some elementsmay be provided with a bend pattern along the bend lines and/or theparts within the bend allowance section to reduce the bend stress. FIG.5 illustrates a plane view and a cross-sectional view of exemplary bendpatterns 300, which may be applied to some of the components. The bendpatterns 300 described above may be used in the support layer 108, thepolarization layer 110, the touch sensor layer 114 and various otherelements of the flexible display 100.

The flexible display 100 may utilize more than one type of bendpatterns. It should be appreciated that a number of bend patterns andthe types of the bend patterns 300 utilized by the components is notlimited. If desired, the depth of the patterns may not be deep enough topenetrate through the component entirely but penetrate only partiallythrough the respective layer. As will be described in further detailbelow, a buffer layer positioned between the base layer 106 and the TFTas well as a passivation layer covering a conductive line may be also beprovided with the bend pattern for reducing bend stress.

Support Member

As mentioned, the support layer 108 may not be present at the bendallowance section to facilitate easier bending of the base layer 106.Absent the support layer 108, however, the curvature at the bendallowance section may be easily altered by external force. To supportthe base layer 106 and maintain the curvature at the bend allowancesection, the flexible display 100 may also include a support member 116,which may also be referred to as a “mandrel.” The exemplary supportmember 116 depicted in FIG. 4 has an elongated body portion and arounded end portion. The base layer 106 and the support member 116 arearranged so that that the rounded end portion of the support member 116is positioned at the underside of the base layer 106 corresponding tothe bend allowance section of the flexible display 100.

In embodiments where a bend portion is provided at an edge of theflexible display 100, the support member 116 can be provided at the edgeof the flexible display 100. In this setting, a part of the base layer106 may come around the rounded end portion of the support member 116and be positioned at the underside the support member 116 as depicted inFIG. 4. Various circuits and components in the inactive area of theflexible display 100, such as drive ICs and interfaces for connectingchip-on-flex (COF) and flexible printed circuit board (FPCB), may beprovided on the base layer 106 that is positioned at the rear side ofthe flexible display 100. In this way, even the components that are notflexible enough to be bent in a bend radius desired by the flexibledisplay 100 can be placed under the active area of the flexible display100.

The support member 116 can be formed of plastic material such aspolycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN),polyethylene terephthalate (PET), other suitable polymers, a combinationof these polymers, etc. The rigidity of the support member 116 formed ofsuch plastic materials may be controlled by the thickness of the supportmember 116 and/or by providing additives for increasing the rigidity.The support member 116 can be formed in a desired color (e.g., black,white, etc.). Further, the support member 116 may also be formed ofglass, ceramic, metal or other rigid materials or combinations ofaforementioned materials.

Size and shape of the rounded end portion of the support member 116 canvary depending on the minimum curvature desired at the bend allowancesection of the flexible display 100. In some embodiments, the thicknessof the rounded end portion and the thickness of the elongated bodyportion may be substantially the same. In other embodiments, theelongated body portion, which has a planar shape, may be thinner thanthe rounded end portion of the support member 116. With a thinnerprofile at the elongated body portion, the support member 116 cansupport the bend allowance section while avoiding unnecessary increasein the thickness in the flexible display 100.

Since the support at the bend allowance section is provided by therounded end portion of the support member 116, the elongated planarportion extending toward the substantially flat portion of the flexibledisplay 100 needs not be extended into the active area. While theelongated body portion can be extended under the active area for variousreasons, the length of the elongated body portion from the rounded endportion towards the opposite end is sufficient so long as it providesenough surface area for securing the support member 116 in a desiredlocation of the flexible display 100.

To secure the support member 116 in the flexible display 100, anadhesive layer 118 may be provided on the surface of the support member116. The adhesive layer 118 may include a pressure-sensitive adhesive, afoam-type adhesive, a liquid adhesive, a light-cured adhesive or anyother suitable adhesive material. In some embodiments, the adhesivelayer 118 can be formed of, or otherwise includes, a compressiblematerial and serve as a cushion for the parts bonded by the adhesivelayer 118. As an example, the constituent material of the adhesive layer118 may be compressible. The adhesive layer 118 may be formed ofmultiple layers, which includes a cushion layer (e.g., polyolefin foam)interposed between an upper and a lower layers of an adhesive material.

The adhesive layer 118 can be placed on at least one of the uppersurface and the lower surface of the elongated body portion of thesupport member 116. When the bend portion of the flexible display 100wraps around the rounded end portion of the support layer 116, anadhesive layer 118 can be provided on both the lower surface (i.e., thesurface facing the rear side) and the upper surface (i.e., the surfacefacing the front side) of the elongated body portion. If desired, anadhesive layer 118 may be provided between the surface of the roundedend portion of the support member 116 and the inner surface of the baselayer 106.

During bending, a part of the flexible display 100 on one side of thesupport member 116 may be pulled toward the support member 116, and thebase layer 106 may be damaged by the highest and the lowest edges of therounded end portion. As such, the height of the adhesive layer 118 andthe support layer 108 between the support member 116 and the base layer106 may be at least equal to or greater than the vertical distancebetween the highest edge of the rounded end portion and the surface ofthe elongate body portion where the adhesive layer 118 is placed. Inother words, the height of the space created by the thickness differencebetween the rounded end portion and the elongated body portion of thesupport member 116 may be equal to or less than the collective thicknessof the support layer 108 and the adhesive layer 118.

Depending on the shape of the support member 116, a thickness of theadhesive layer 118 on the upper and the lower surfaces of the elongatedbody portion may be different. For instance, the elongated body portion,which is thinner than the rounded end portion, may not be at the centerof the rounded end portion of the support member 116. In such cases, thespace on one side of the support member 116 may be greater than thespace on the opposite side.

In another example, the lowest edge of the rounded end portion may bein-line with the bottom surface of the elongated body portion such thatthe space is provided only on one side of the elongated body portion. Insuch cases, the adhesive layer 118 on one side of the elongated bodyportion of the support member 116 can be thicker than the one on theopposite side. It should be appreciated that the dimensions of thesupport member 116 in FIG. 4 may be exaggerated for the purposes ofsimpler explanation.

Exemplary Arrangement

FIGS. 6A, 6B and 6C are simplified cross-sectional view showing anexemplary arrangement of elements in various embodiments of the flexibledisplay 100. In one suitable configuration, the thickness of the roundedend portion and the elongated body portion of the support member 116Amay be substantially the same as illustrated in FIG. 6A. Such a supportmember 116A can be formed of the plastic materials mentioned above. Thesupport member 116A may also be formed of a folded thin sheet metal(e.g., SUS). In this case, the folded edge of the sheet metal can serveas the rounded end portion of the support member 116A. Even when a sheetmetal is used to form the support member, the rounded end portion canhave greater thickness than the elongated body portion. For instance,pressure can be applied on the part of the folded metal sheet for theelongated body portion to make that portion thinner than the foldededge.

In FIG. 6A, the adhesive layer 118A is illustrated as being applied onthe upper, the lower surface and the surface of the rounded end portionof the support member 116A. As the thickness of the support member 116Aat the rounded end portion and the elongated body portion is about thesame, the thickness of the adhesive layer 118A may have a substantiallyuniform thickness on the surface of the support member 116A. However, itshould be noted that the adhesive layer 118A can be thinner and/orthicker at selective parts of the support member 116A.

In another suitable configuration, the elongated body portion of thesupport member 116 is thinner than its rounded end portion. In thisregard, the bottom surface of the elongated body portion is in-line withthe lowest edge of the rounded end portion, providing a support member116B with a flat bottom as depicted in FIG. 6B. In this exemplaryconfiguration, the support members 116B may be formed of one or acombination of aforementioned plastic materials (e.g., polycarbonate).Also, the adhesive layer 118B provided on the upper surface of theelongated body portion is thicker than the adhesive layer 118B providedon the bottom surface of the elongated body portion of the supportmember 116B. The adhesive layer 118B on the upper surface of theelongated body portion may include a cushion layer described above whilethe adhesive layer 118B on the lower surface does not.

In yet another suitable configuration shown in FIG. 6C, neither the topnor the bottom surfaces of the elongated body portion of the supportmember 116C is in-line with the highest/lowest edges of the roundedportion. The support members 116C may be formed of one or a combinationof aforementioned plastic materials (e.g., polycarbonate). In thisexample, the elongated body portion is off-centered (i.e., closer to thelowest edge of the rounded portion), and the adhesive layer 118C on theupper surface of the elongated body portion is thicker than the adhesivelayer 118C on the lower surface. The adhesive layer 118C on the uppersurface of the elongated body portion may include a cushion layerdescribed above while the adhesive layer 118C on the lower surface doesnot.

In the exemplary configurations depicted in FIGS. 6A-6C, the supportlayer 108 on the upper side of the support member 116 is extendedfurther out toward the bend allowance section than the encapsulation 114there above. In other words, a part of the base layer 106 toward thebend allowance section is not covered by the encapsulation 114, butprovided with the support layer 108 thereunder. The extra length of thesupport layer 108 can help in keeping a steady rate of curvature in thebend allowance section. The edge of the support layer 108 under thesupport member 116 may be shifted away from the bend allowance section.In some embodiments, the edge of the support layer 108 toward the bendallowance section can be provided with a flange, which extends evenfurther out toward the bend allowance section as shown in FIG. 6A. Inone example, the flange may be made by cutting, or otherwise patterning,the support layer 108 to have a tapered edge. In another example, theflange can be provided by stacking at least two support layers withtheir edges shifted from each other. While omitted in FIGS. 6B and 6C,the flange can be provided in those embodiments as well.

It should be appreciated that the configurations described above inreference to FIGS. 6A-6C are merely illustrative. Adhesive layers havingthe same thickness can be provided on the upper and the lower surfacesof the support member regardless of the position of the elongated bodyportion. Further, adhesive layers on both the upper surface and thelower surface of the support member can include a cushion layer.

Wire Trace

Several conductive lines are included in the flexible display 100 forelectrical interconnections between various components therein. Thecircuits fabricated in the active area and inactive area may transmitvarious signals via one or more conductive lines to provide a number offunctionalities in the flexible display 100. As briefly discussed, someconductive lines may be used to provide interconnections between thecircuits and/or other components in the central portion and the bendportion of the flexible display 100.

As used herein, the term conductive lines broadly refers to a trace ofconductive path for transmitting any type of electrical signals, powerand/or voltages from one point to another point in the flexible display100. As such, conductive lines may include source/drain electrodes ofthe TFTs as well as the gate lines/data lines used in transmittingsignals from some of the display driving circuits (e.g., gate driver,data driver) in the inactive area to the pixel circuits in the activearea. Likewise, some conductive lines, such as the touch sensorelectrodes, pressure sensor electrodes and/or fingerprint sensorelectrodes may provide signals for sensing touch input or recognizingfingerprints on the flexible display 100. Furthermore, conductive linescan provide interconnections between elements of the active area in thecentral portion and elements of the secondary active area in the bendportion of the flexible display 100. It should be appreciated that thefunctionalities of conductive lines described above are merelyillustrative.

Conductive lines in a flexible display 100 should be carefully designedto meet various electrical and non-electrical requirements. Forinstance, a conductive line may have a specific minimum electricalresistance level, which may vary depending on the type of signals to betransmitted via the conductive line. Some conductive lines may be routedfrom the substantially flat portion to the bend portion of the flexibledisplay 100. Such conductive lines should exhibit sufficient flexibilityto maintain its mechanical and electrical robustness. To this end, someconductive lines of the flexible display 100 may have a multi-layeredstructure.

FIGS. 7A and 7B each illustrates exemplary stack structure of themulti-layered conductive line. Referring to FIG. 7A, the conductive line120 has a multi-layered structure in which the primary conductive layer122 is sandwiched between the secondary conductive layers 124. Theprimary conductive layer 122 may be formed of material with a lowerelectrical resistance than that of the secondary conductive layer 144.Non-limiting examples of the materials for the primary conductive layer122 includes copper, aluminum, transparent conductive oxide, or otherflexible conductors.

The secondary conductive layer 124 should be formed of conductivematerial that exhibits sufficiently low ohmic contact resistance whenformed in a stack over the primary conductive layer 122. Low ohmiccontact resistance between the conductive layers is not the only factorin the selection of materials for the conductive layers in themulti-layered conductive line 120. While meeting the stringentelectrical and thermal requirements (e.g., resistance, heat generation,etc., the materials of the conductive line 120 should also satisfy theminimum mechanical stress requirement (e.g., Young's modulus). That is,both the primary conductive layer 122 and the secondary conductive layer124 should be formed of materials exhibiting sufficient flexibility.

Accordingly, in some embodiments, at least some of the conductive lines120 of the flexible display 100 may be formed with two or more of layersselected from aluminum (Al), titanium (Ti), molybdenum (Mo), Copper (Cu)layers. Examples of such combination include an aluminum layersandwiched between titanium layers (Ti/Al/Ti), an aluminum layersandwiched between upper and lower molybdenum layers (Mo/Al/Mo), acopper layer sandwiched between titanium layers (Ti/Cu/Ti) and a copperlayer sandwiched between upper and lower molybdenum layers (Mo/Cu/Mo).Of course, other conductive materials can be used for theprimary/secondary conductive layers.

Electronic device employing the flexible display 100, for instance awearable electronic device or a water submergible electronic device, mayexpose the flexible display 100 in a humid environment. In some cases,moist can reach the conductive line 120. Dissimilar metals and alloyshave different electrode potentials, and when two or more come intocontact in an electrolyte, one metal acts as anode and the other ascathode. The electro-potential difference between the dissimilar metalsaccelerates corrosion on the anode member of the galvanic couple, whichwould be the primary conductive layer 122 in the multi-layeredconductive line 120 (e.g., Al layer in the Ti/Al/Ti stack). The anodemetal dissolves into the electrolyte, and deposit collects on thecathodic metal.

When using a multi-layered conductive line 120 described above, anysurface that exposes both the primary conductive layer 122 and thesecondary conductive layer 124 may become a galvanic corrosioninitiation point. Accordingly, in some embodiments of the flexibledisplay 100, at least some conductive lines 120 is provided with astructure in which the outer surface of the primary conductive layer 122is surrounded by the secondary conductive layer 124 as shown in FIG. 7B.Such a configuration hinders the electrolyte from being in contact withboth the primary conductive layer 122 and the secondary conductive layer124, thereby minimizing loss of the primary conductive layer 122 bygalvanic corrosion.

Such a multi-layered conductive lines 120 can be created by firstdepositing the material for the primary conductive layer 122 (e.g., Al)over the secondary conductive layer 124 (e.g., Ti). Here, the secondaryconductive layer 124 underneath the primary conductive layer 122 mayhave greater width. Etch resist material is formed over the stack ofthese two layers and etched (e.g., dry etch, wet etch, etc.) to form theconductive line in a desired trace. After striping the etch resistancematerial, another layer of secondary conductive layer 124 (i.e., Ti) isdeposited over the patterned structure (i.e., Ti/Al). The width of thesecondary conductive layer 124 deposited over the primary conductivelayer 122 may be greater than the width of the primary conductive layer122 to cover the outer surface of the primary conductive layer 122.Another round of etching and striping of the etch resistance material isperformed to form the stack of a multi-layered conductive line in adesired conductive line trace design. It should be understood that themulti-layered conductive line formation processes described above aremerely an example. Accordingly, some processes may be added and/orskipped in making a multi-layered conductive line.

A trace design of a conductive line is an important factor, which canaffect the conductive line's electrical and mechanical properties. Tomeet the electrical and mechanical requirements, some portion of aconductive line may be configured differently from another portion ofthe conductive line. As such, a portion of a conductive line at or nearthe bend allowance section of the flexible display 100 may be providedwith several features for bend stress management.

Bend stress management of the insulation layers near the conductive lineis just as important as the managing the strain of the conductive lineitself. Various insulation layers, such as the buffer layer 126, thepassivation layer 128, a gate insulation layer (GI layer) and aninterlayer dielectric layer (ILD layer) positioned below and/or abovethe conductive line 120 may include a layer of inorganic materials.Layers that are formed of inorganic material, for instance a siliconoxide layer and a silicon nitride layer, are generally more prone tocracks than the metal layers of the conductive line. Even when theconductive lines have a sufficient flexibility to cope with the bendstress without a crack, some of the cracks initiated from the insulationlayer can propagate into the conductive lines and create spots of poorelectrical contacts in the flexible display 100.

In addition to applying a trace design for reducing bend stress on aconductive line, some of the insulation layers above and/or below thelayer of conductive line may be patterned according to the trace designof the conductive line to minimize the chance of cracks. Variousinsulation layer patterning methods, such as wet etching and/or dryetching processes, can be used to form a trace of insulation layer thatcorresponds to the trace of a conductive line. Lack of insulation layer,especially the inorganic material based insulation layer around thetrace of a conductive line not only lowers the chance of crackgeneration, but it also cuts off the path for a crack propagation. Forconvenience of explanation, a trace of conductive line 120 and a traceof insulation layers covering at least some part of the conductive line120 are collectively referred to as the “wire trace” in the followingdescription.

Trace Design

As mentioned, a trace design for the conductive line and the insulationlayer covering the conductive line plays an important role in increasingthe robustness of the wire trace. Numerous parameters, ranging from athickness and a width of a wire trace to a length and a fan-out angle ofa wire trace segment with respect to the bending direction of theflexible display 100, are associated with the wire trace design. Inaddition to the aforementioned parameters, various other parametersregarding the conductive line 120 and the insulation layer trace arespecifically tailored based on the placement and the orientation of thewire trace within embodiments of the flexible display 100.

Strain on a wire trace from the bend stress will be greater as thedirection in which the wire trace extends is more aligned with thetangent vector of the curvature. In other words, a wire trace willwithstand better against the bend stress if the length of a wire tracesegment being parallel to the tangent vector of the curvature isreduced. No matter which direction the wire trace is extended to, therewill always be a portion in the wire trace that is measurable in thebending direction. However, a length for each continuous measurableportion (i.e., a segment) being aligned parallel to the bendingdirection can be reduced by employing a strain-reducing trace design inthe wire trace.

FIG. 8 illustrates some of the exemplary strain-reducing trace designs.Any one or more of a sign-wave, a square-wave, a serpentine, asaw-toothed and a slanted line trace designs illustrated in FIG. 8 canbe used for wire traces of the flexible display 100. Employing such astrain-reducing trace design increases the portion of the wire tracearranged in a slanted orientation with respect to the tangent vector ofthe curvature. This, in turn, limits the length of the wire tracesegment extending in a straight line parallel to the bending direction.

Since the cracks in the wire trace by bending of the flexible displaygenerally initiate from an inorganic insulation layer, it is imperativethat the length of the insulation layer trace being aligned with thetangent vector of the curvature is also minimized. In the single linestrain-reducing designs, the width and the shape of the conductive linetrace as well as the width of the patterned inorganic insulation layersinterfacing with the surface of the conductive line trace should be keptminimal.

The strain-reducing trace designs illustrated in FIG. 8 are merelyexemplary, and other trace designs for reducing the length of a wiretrace segment parallel to the bending direction may be used in variousembodiments of the flexible display 100. Further, it should be notedthat some wire traces may adopt different strain-reducing trace designfrom other wire traces in a flexible display 100 depending on theirelectrical and/or mechanical requirements. For instance, astrain-reducing trace design used for a data signal line may bedifferent from a strain-reducing trace design used for a power line.

To further improve robustness, a wire trace may employ a trace design inwhich the wire trace repeatedly splits and converges back in a certaininterval. In other words, a wire trace includes at least two sub-tracesarranged to form a trace design resembling a chain with a series ofconnected links. The angles of split and merge define the shape of eachlink, which allows to limit the length of the wire trace segmentmeasurable in straight line parallel to the bending direction.

Referring to FIG. 9A, the conductive line 120 includes sub-trace A andsub-trace B, which are split away from each other and merge back at eachjoint X. Between the first joint X(1) and the second joint X(2), a partof the sub-trace A is extended for a predetermined distance in a firstdirection angled away from the tangent vector of the curvature, andanother part of the sub-trace A is extended in a second direction. Thesub-trace B is arranged in a similar manner as the sub-trace A, but in amirrored orientation in reference to the tangent vector of thecurvature. The distances and directions in which the sub-traces arearranged between the two adjacent joints X define the shape and the sizeof the link in the chain as well as the open area surrounded by thesub-traces. In this example, the shape of the conductive line 120between the joint X(1) and X(2) (i.e., link) has a diamond shape with anopen area surrounded by the sub-trace A and the sub-trace B. Withadditional joints X, the conductive line 120 forms a chain of diamondshaped links, and thus the trace design may be referred to as thediamond trace design.

Compare to the non-split strain-reducing trace designs shown in FIG. 8,the strain-reducing trace design shown in FIG. 9A can providesignificant advantages in terms of electrical property. For instance,the wire trace provided with the split/merge trace design can providemuch lower electrical resistance than the wire traces employing themountain trace design, the sign-wave trace designs or other single linestrain-reducing trace designs of FIG. 8. In addition, sub-traces canserve as a backup electrical pathway in case one of the sub-traces isdamaged or severed by cracks.

The insulation layers covering the surfaces of the conductive line 120is also patterned in a trace design corresponding to the trace design ofthe conductive line 120. As such, the open area surrounded by thesub-trace A and the sub-trace B is free of the inorganic insulationlayer(s), or has thinner inorganic insulation layer(s) than the areasunder and/or above the trace of conductive line 120. As such, the lengthof the insulation layer trace measurable in straight line parallel tothe bending direction can be limited to reduce the chance of crackinitiation and propagation.

Various additional factors must be considered for the strain-reducingtrace designs based on a plurality of sub-traces. The split/merge anglesand the length of each sub-traces between two adjacent joints X shouldprovide an offset for the inorganic insulation layer at the joints X andat the outer corners where the sub-trace changes its direction betweentwo adjacent joints X. To put it in another way, the open area, which issurrounded by the split sub-traces between two joints X of the wiretrace, should have a size and a shape to minimize the length in which aninorganic insulation layer trace of the wire trace extending parallel tothe bending direction.

In the diamond trace design depicted in FIG. 9A, the buffer layer 126and the passivation layer 128 covering the trace of the conductive line120 are patterned with a predetermined margin from the outer trace(i.e., outer edge) of the conductive line 120. Other than the insulationlayers with the predetermined margin remaining to cover the conductiveline 120, the open area surrounded by the sub-traces A and B, which isdenoted as FA2, is free of the insulation layers. As such, a trace ofinsulation layers are formed in accordance with the trace design of theconductive line 120. The length of the open area without the insulationlayers measured in orthogonal direction from the bending direction isgreater than the width of the inorganic insulation layer trace at thejoint X measured in the same direction. In this setting, the open areaFA2 surrounded by the sub-traces A and B as well as the area next to thejoint X can be free of the inorganic insulation layers, or otherwiseprovided with a reduced number of inorganic insulation layers.

Referring to FIG. 9A, the insulation layer free area FA1 prohibits theinsulation layer of the sub-trace A and the sub-trace B between the twojoints X(1) and X(2) to be extended in a continuous straight line.Similarly, the insulation layer free area FA2 prohibits the insulationlayer between the two joints X(1) and X(2) to be extended in acontinuous straight line. Accordingly, the length of each segment of theinsulation layer trace being aligned to the tangent vector of thecurvature is minimized.

Further reduction in the length of the insulation layer trace aligned tothe tangent vector of the curvature can be obtained by reducing thewidth of the conductive line 120 and the margin of the insulation layerbeyond the edge of conductive line 120. It should be noted that theamount of reduction in the width of conductive line 120 is limited withthe single line strain-reducing trace designs depicted in FIG. 8 becausethe reduction of conductive line width can make its electricalresistance too high for its particular use within the flexible display100. With the split/merge trace design of FIG. 9A, however, the width ofthe conductive line 120 and the insulation layer trace can be reducedwhile providing sufficient electrical property.

Greater split/merge angle of the sub-traces with respect to the bendingdirection may allow to reduce the lengths of the conductive line 120 andthe insulation layer trace extending along the tangent vector of thecurvature to a greater extent. Accordingly, a lower chance of crackinitiation may be afforded in the wire trace by selectively increasingthe split/merge angle of sub-traces at high bend stress regions.

It should be noted that the split angle of the sub-traces can affect thedistance between the two adjacent joints X in the diamond trace design.The distance between the joints X need not be uniform throughout theentire wire trace. The intervals at which the trace splits and mergescan vary within a single trace of wire based on the level of bend stressexerted on the parts of the wire trace. The distance between the jointsX may be progressively shortened down for the parts of the wire tracetowards the area of the flexible display 100 subjected to higher bendstress (e.g., area having smaller bend radius, area having larger bendangle). Conversely, the distances between the joints X can progressivelywiden out towards the area subjected to lower bend stress.

Even with the strain-reducing trace design, the inevitable bend stressremains at certain points of the trace (i.e., stress point). Thelocation of stress point is largely dependent on the shape of the traceas well as the bending direction. It follows that, for a given bendingdirection, the wire trace can be designed such that the remaining bendstress would concentrate at the desired parts of the wire trace. Knowingthe location of the stress point in the wire trace, a crack resistancearea can be provided to the stress point to make the wire trace lastlonger against the bend stress.

Referring back to FIG. 9A, when a wire trace having the diamond tracedesign is bent in the bending direction, the bend stress tends to focusat the angled corners (i.e., the vertexes of each diamond shaped link),which are denoted as the stress point A and stress point B. As such,cracks tends to initiate and grow between the inner and outer edges ofthe wire trace. For instance, at the stress points A, a crack mayinitiate from the inner trace line 120(IN) and grow toward the outertrace line 120(OUT). Similarly, a crack may initiate from the outer wiretrace line 120(OUT) and grow toward the inner trace line 120(IN) at thestress points B.

Accordingly, the width of the conductive line 120 at the stress points Acan be selectively increased to serve as the crack resistance area. Asdepicted in FIG. 9A, the widths (WA, WB) of the conductive line 120 atthe stress points A and B, which are measured in the directionperpendicular to the bending direction, may be longer than the width (W)of the conductive line 120 at the parts between the stress points A andB. The extra width at the stress points can make the conductive line 120hold out longer before a complete severance in the conductive line 120occurs by the growth of a crack at the stress points.

It should be reminded that the length for the continuous portion of theinsulation layer trace being aligned to the bending direction should bekept minimal. Increasing the width of the conductive line 120 at thestress points A and B may necessitate increase in the width of theinsulation layer trace at the respective area, which results inlengthening the insulation layer trace being aligned parallel to thebending direction.

Accordingly, in some embodiments, the width of the conductive line 120measured in the direction perpendicular to the tangent vector of thecurvature at the stress points A ranges from about 2.5 μm to about 8 μm,more preferably, from about 3.5 μm to about 6 μm, more preferably fromabout 4.5 μm to about 8.5 μm, and more preferably at about 4.0 μm. Thewidth of the conductive line 120 at the stress points B should also bemaintained in the similar manner as the width of the conductive line 120at the stress points A. As such, the width of the conductive line 120 atthe stress points B may range from about 2.5 μm to about 8 μm, morepreferably, from about 3.5 μm to about 6 μm, more preferably from about4.5 μm to about 8.5 μm, and more preferably at about 4.0 μm. Since thesub-trace A and the sub-trace B merges at the stress point B, the widthof the conductive line 120 at the stress points B may be longer thanwidth at the stress points A.

In some embodiments, one of the inner trace line 120(IN) and the outertrace line 120(OUT) may not be as sharply angled as the other trace lineat the stress points A to minimize the chance of crack initiating fromboth sides. In the embodiment depicted in FIG. 9A, the inner trace line120(IN) is more sharply angled than the outer trace line 120(OUT) at thestress points A. However, in some other embodiments, the outer traceline 120(OUT) may be more sharply angled than the inner trace line120(IN) at the stress points A. In both cases, the less sharply angledtrace line can simply be more rounded rather than being a straight lineas the outer trace line 120(OUT) depicted in FIG. 9A. Further, both theinner trace line 120(IN) and the outer trace line 120(OUT) at the stresspoints A can be rounded.

The wire trace may split into additional number of sub-traces, resultingseries of links arranged in a grid-like configuration. As an example, awire trace can be configured as a web of diamond trace shapes asillustrated in FIG. 9B. Such a trace design is particularly useful for awire trace that transmit a common signal to multiple points or for awire trace that require a very low electrical resistance. For example, aVSS line and a VDD line in the flexible display 100 may have thegrid-like trace design, especially if such lines are arranged to crossover a bend allowance section. Neither the number of sub-traces nor theshapes of the sub-traces of the grid-like trace design are particularlylimited as the exemplary design depicted in FIG. 9B.

In some embodiments, the grid width can be reduced or increased inbetween two ends within the flexible display 100. Also, the grid-likewire trace shown in FIG. 9B can converge back to form the diamond traceshown in FIG. 9A or to form a non-split strain-reducing trace design. Insome cases, the size of each diamond-shaped trace of a grid-like wiretrace may be larger than the size of each diamond-shaped trace of adiamond-chain trace to reduce the resistance.

Wire Trace Arrangement

Due to the portions angled away from the bending direction, a wire tracewith a strain-reducing trace design may necessitate a larger routingarea within the flexible display 100. In embodiments where a non-displayarea at the edge of the flexible display 100 is bent, the increase inthe routing area for accommodating the wire traces can actually increasethe size of the inactive area to be hidden under a masking.

Accordingly, wire traces applied with a strain-reducing trace design maybe arranged to facilitate tight spacing between adjacent wire traces.For instance, two adjacent wire traces with a strain-reducing tracedesign may each include a non-linear section, which would have a convexside and a concave side. The two adjacent wire traces can be arranged inthe flexible display such that the convex side of the non-linear sectionin the first wire trace is positioned next to the concave side thenon-linear section in the second wire trace. Since the spacing betweenthe two adjacent wire traces is limited by the shape and the size of thewire traces, the non-linear section in the strain-reducing trace designof the first wire trace may be larger than the non-linear section in thestrain-reducing trace design of the second wire trace. Of course, one ofthe first wire trace and the second wire trace may have a differentstrain-reducing trace design to better accommodate the non-linearsection of the other wire trace.

In some instances, two or more wire traces arranged next to each othermay each be applied with a strain-reducing trace design, and each of thewire traces may have a plurality of indented sections and distended. Insuch cases, the wire traces can be arranged such that the distendedsection of one of the wire traces to be positioned next to the indentedsections of the adjacent wire trace.

FIG. 10 illustrates an exemplary arrangement of multiple wire traces,each having the diamond trace design described above. The split of thesub-traces widens the layout of the wire trace to create the distendedsection, whereas merging of the sub-traces narrows the layout of thewire trace to create the indented section. Accordingly, in terms of itslayout, the indented section of the wire trace is at the joint X,whereas the distended section of the wire trace is at the point wherethe split/merge angles of the sub-traces change between two adjacentjoints X.

As shown in FIG. 10, position of the joints X in a first wire trace andthe joints X in a second wire trace are arranged in a staggeredconfiguration. In this arrangement, the vertexes of the diamond shapedlink at the distended section in the first wire trace are positionednext to the joints X at the indented sections of the adjacent wiretraces. Such a staggered arrangement of the wire traces may help inlowering the electrical noises on the wire traces due to close proximitybetween the wire traces, and thus the distance between the wire tracescan be reduced. Even a tight spacing between the wire traces may bepossible by arranging the distended section of a wire trace to bepositioned closer toward the indented section of the adjacent wiretrace. For instance, the vertexes at the wide parts of one wire race canbe placed in the open area FA1, which is created by the split/mergeangle and the length of the sub-trace in the adjacent wire trace. Assuch, the staggered arrangement allows to maintain certain minimaldistance between the wire traces while reducing the amount of spacetaken up by the wire traces.

Patterned Insulation Layer

As mentioned, it should be noted that cracks primarily initiate from theinorganic insulation layers. Accordingly, propagation of cracks can besuppressed by selectively removing inorganic insulation layers from theareas prone to cracks. To achieve this, one or more inorganic insulationlayers and/or stack of insulation layers including a layer of inorganicmaterial can be selectively etched away at various parts of the flexibledisplay 100.

For example, the insulation layer under the conductive line 120 can beetched away. The insulation layer under the conductive line 120 may bethe buffer layer 126, which may include one or more layers of inorganicmaterial layers. The buffer layer 126 may be formed of one or morelayers of a SiNx layer and a SiO2 layer. In one suitable configuration,the buffer layer 126 may be formed of alternating stacks of a SiNx layerand a SiO2 layer. The buffer layer 126 is disposed on the base layer126, but under the TFT.

To facilitate easier bending of the flexible display 100, a part of thebuffer layer 126 may etched away in the bend portion of the flexibledisplay 100. Accordingly, the buffer layer 126 formed on thesubstantially flat portion of the base layer 106 may be thicker than thebuffer layer 126 over the bend portion of the base layer 106. When thebuffer layer 126 is formed in a stack of multiple sub-layers, the bufferlayer 126 in the substantially flat portion of the flexible display 100may include one or more additional sub-layers than the buffer layer inthe bend portion of the flexible display 100.

For example, the buffer layer 126 in the substantially flat portion mayinclude multiple stacks of a SiNx layer and a SiO2 layer, and the bufferlayer 126 in the bend portion includes a single stack of a SiNx layerand a SiO2 layer. It is also possible to have only a single layer ofeither a SiNx layer or a SiO2 layer in some part of the bend portion. Inone suitable configuration, each SiNx layer and SiO2 layer in the bufferlayer 126 may have a thickness of about 1000 Å. As such, the thicknessof the buffer layer 126 in the bend portion of the flexible display mayrange from about 100 Å to about 2000 Å.

In the substantially flat portion of the flexible display 100,additional layer of inorganic layer may be provided immediately belowthe semiconductor layer of the TFT, which may be referred to as theactive buffer. In some embodiments, an inorganic layer, which is mostclosely positioned under the active layer of the TFT, may be muchthicker than the individual inorganic layers of the buffer layer 126.

The buffer layer 126 in the bend allowance section may be etched evenfurther to expose the base layer 106 while leaving the buffer layer 126intact under the conductive line 120. In other words, a recessed areaand a protruded area are provided in the bend portion of the flexibledisplay 100. The protruded area includes the buffer layer 126 providedon the base layer 106, whereas the recessed area has the base layer 106exposed without the buffer layer 126 disposed thereon.

In one exemplary configuration shown in FIG. 11A, the conductive line120 is positioned on the protruded area, and the passivation layer 128is positioned over the conductive line 120 on the protruded area.Although the passivation layer 128 may be temporarily deposited over therecessed area, the passivation layer 128 can be removed from therecessed area by a dry etch or a wet etch process. As such, the recessedarea can be substantially free of the passivation layer 128. Whenetching the passivation layer 128 from the recessed area, part of thebase layer 106 can be etched as well. Accordingly, the thickness of thebase layer 106 at the recessed area can be lower than that of the baselayer 106 elsewhere in the flexible display 100. When the buffer layer126 is etched away as shown in FIG. 11A, propagation of crack from onepart of the buffer 126 to another part of the buffer layer 126 can behindered by the space in the recessed area. Similarly, propagation ofcracks by the passivation layer 128 is also hindered by the space of therecessed area. Accordingly, damage to the conductive line 120 bypropagation of cracks can be reduced.

In another suitable configuration shown in FIG. 11B, the recessed areaincludes the base layer 106 that is etched to a certain depth, and theconductive line 120 is deposited on the base layer 106 of the recessedarea. In this setting, the portion of the conductive line 120 isdisposed within the base layer 106. Some part of the conductive line 120is also deposited on a part of the buffer layer 126 that provides theprotruded area. A passivation layer 128 can be deposited over theconductive line 120, and then etched away from the recessed area toexpose the conductive line 120 in the recessed area.

Accordingly, the passivation layer 128 remains on the conductive line120 positioned on the protruded area. In this configuration, thepassivation layer 128 remaining on the buffer layer 126 can inhibitgalvanic corrosion as it covers the cross-sectional side surface of themulti-layered conductive line 120. While cracks generated from thebuffer layer 126 may penetrate to the conductive line 120 on the wall ofhollow space in the buffer layer 126, but reaching the part of theconductive line 120 positioned within the base layer 106 will bedifficult.

When the conductive line 120 has the multi-layered structure discussedabove, the part of the conductive line 120 in the recessed area needsnot be covered by the passivation layer 128. With the passivation layer128 removed from the surface of the conductive line 120 in the recessedarea, crack propagation from the passivation layer 128 can also beprevented. Further, galvanic corrosion generally starts from the edge ofthe conductive line 120 on the buffer layer, and thus the passivationlayer 128 covering the edge of the conductive line 120 on the buffer 126may not be needed if the distance between the conductive line 120 on thebuffer layer 126 and the conductive line 120 in the base layer 106 issufficiently spaced apart from each other. The configurations shown inFIGS. 11A and 11B may be used for the wire traces in the bend allowancesection with the strain-reducing trace patterns of FIGS. 8, 9A and 9B.In addition to the bend allowance section, in some embodiments, thepatterned insulation layer may also be provided in the routing areabetween the active area and the bend allowance section as well as therouting area between the COF bonding area and the bend allowancesection.

Further, the patterned insulation layer described above can be providedin the active area. However, removal of inorganic insulation layers nearthe TFTs of the flexible display 100 may affect the electricalcharacteristic of components in the flexible display 100. For instance,undesired threshold voltage shift of TFTs may result when some part ofthe buffer layer 126 is removed. In order to maintain the stability ofthe TFTs, an additional shield metal layer can be formed under thesemiconductor layer of the TFTs. The shield metal layer may be under thebuffer layer 126 or interposed between the inorganic layers of thebuffer layer 126. In some embodiments, the shield metal layer may beelectrically connected to the source electrode or gate electrode of theTFTs.

In addition to the patterning of insulation layers in various parts ofthe flexible display 100, other structural elements can be removed orsimplified in some areas of the flexible display 100 to facilitatebending. For example, the touch sensor layer 112, the polarization layer110 and the likes may be absent in the bend area of the flexible display100. Absence or simplification of these components and the layers wouldcreate a number of uneven surfaces where the wire trace may need tocross.

When a wire trace is laid over such an uneven surface, some parts of thewire trace may be placed on a different plane level from another partsof the wire trace. As the parts are on different plane levels, theamount and direction of bend stress and the strain resulting from thebend stress can differ even among the parts of the wire trace. Toaccommodate the difference, a strain-reducing trace design for the wiretraces can include a modified trace design for the portion of the wiretrace on the uneven surfaces.

FIG. 12A is an enlarged cross-sectional view showing an exemplarybackplane configuration for a flexible display 100, in which severalinsulation layers are removed from the bend portion to facilitate morereliable bending.

Several organic and inorganic layers may be formed in between the baselayer 106 and the OLED element layer 102. In this particular example,alternating stacks of SiNx and SiO2 layers can be disposed on the baselayer 106 to serve as the buffer layer 126. The semiconductor layer of aTFT may be sandwiched by an active-buffer layer and a gate insulationlayer that are formed of SiO2 layer. The gate of the TFT is disposed onan interlayer dielectric layer (ILD), and the source/drain of the TFThaving the multi-layered structure as discussed above is sandwichedbetween the ILD and a passivation layer. Here, the ILD may be formed ofa stack of SiNx and SiO2, and the passivation layer is formed of SiNx.Then, a planarization layer is disposed over the passivation layer sothat the anode for the OLED can be disposed thereon.

As mentioned above, use of the strain-reducing trace design is not justlimited to the part of the wire traces within the bend portion. Also,the strain-reducing trace design can be applied to the part of the wiretraces in the routing areas outside the bend allowance section. Usingthe strain-reducing trace design for the wire trace in such routing areacan afford increased protection to the wire trace against the bendstress.

In the routing area, however, several layers of organic and/or inorganicmaterial layers between the base layer 106 and the OLED element layer102 may be absent to facilitate bending of the flexible display 100.Such organic and/or inorganic layers, including but not limited to theILD, the gate insulation layer, buffer layer, passivation layer,planarization layer, etc. may not be present in the bend portion of theflexible display 100. Some of these layers may have been removed fromthe area by several etching processes.

By way of example, several insulation layers on the buffer layer 126 maybe etched by a first etch process EB1, which is followed by the secondetch process EB2 that etches away the active buffer and a part of thebuffer layer 126 (e.g., a stack of a SiNx layer and a SiO2 layer). Theseetching processes create multiple stepped regions as shown in FIG. 12A,with one or more of vertically sloped surfaces and horizontally leveledsurfaces, where the wire trace is disposed thereon. The wire trace laidover the vertically sloped surfaces and horizontally leveled surfaceswould have several bent spots, such as EB1 area and EB2 area.

When bending the flexible display 100 in the bending direction, the wiretrace may experience more strain at or near the stepped region. Numeroustests and experiments indicate that the chance of a crack is especiallyhigh in the wire trace crossing over the stepped region between the EB1area and the EB2 area. Accordingly, in some embodiments, thestrain-reducing trace design for the wire trace has a reinforced portionat or near the stepped region between a high-leveled surface and alow-leveled surface provided by insulation layers of the flexibledisplay.

In the example shown in FIG. 12B, the wire trace has a simple straightline trace at its both ends. However, the part of the conductive line120 that crosses over the bent areas EB1 and EB2 is reinforced with amodified trace design. At the modified portion, the conductive line 120is provided with a wider width extra width WR to ensure theperseveration of the conductive line 120 even if cracks initiate fromthe insulation layer near EB1 and EB2 areas. The distance DR in whichthe conductive line 120 is provided with the modified trace designdepends on the thickness of the insulation layers etched by the etchprocesses as well as the distance between the first leveled surface(e.g., plane level at EB1) and a second leveled surface (e.g., planelevel at EB2).

Past the modified portion (i.e., reinforced portion), the wire trace isillustrated as having the strain-reducing trace design (i.e., diamondtrace design), which is previously described with FIG. 9A. It should beappreciated that the strain-reducing trace design of the wire traceapplied with the modified portion is not limited to the strain-reducingtrace design depicted in FIG. 12B. Various embodiments of thestrain-reducing trace design can include a modified trace design for theportion of the wire trace corresponding to the stepped areas of twodifferently leveled surfaces.

While this may not always be the case, the routing areas adjacent to thebend allowance section may be the substantially flat portions of theflexible display 100. In such cases, the EB1 and EB2 areas would bepositioned at or just outside start of the bend allowance section in thebend portion, and the wire trace may be provided with the reinforcedportion in its trace design.

The increased width WR of the reinforced conductive line 120 portion mayserve its purpose well at or near the beginning and the end of the bendallowance section where the curvature is relatively small. The widerwidth WR of the wire trace and the length in which the modified traceportion is applied in the wire trace can increase the length of the wiretrace that is aligned parallel to the bending direction. This would bemake the wire trace harder to hold out against the bend stress at theregion with greater bend radius.

For this reason, the distance DR in which the reinforced portion isshould be limited such that the reinforced conductive line portion doesnot extend too much toward the bend allowance section. Accordingly, thedistance DR of the reinforced conductive line portion may be limitedsuch that the trace design of the reinforced conductive line portiondoes not extend beyond the bend allowance section where it is bent morethan a predetermined threshold bend angle. By way of an example, thereinforced conductive line portion may not extend beyond the point whereit is 30° curved away from the tangent plane of the curvature. Thethreshold bend angle may be less than 20°, for example 10°, and morepreferably less than 7°.

The wire trace, which is provided with the reinforced portion at thestepped areas, may extend across the bend allowance section and routedto pads for COF or other components of the flexible display 100. In suchinstances, additional stepped region (similar to EB1 and EB2) may existat or near the opposite end of the bend allowance section. Theconductive line at or near such bent spots may be reinforced in thesimilar manner as the modified portion of the wire trace at the oppositeend as shown in FIG. 12B. If desired, the reinforced conductive lineportion at or near the stepped regions at the opposite ends of the bendallowance section may have a different shape as depicted in FIG. 12B.

Areas near the scribing line and/or chamfering line of the flexibledisplay 100 may be another spots vulnerable to cracks. For instance,cracks can initiate from the insulation layers during scribing the baselayer 106 or chamfering a portion of the base layer 106. The cracksgenerated at the far end of the flexible display 100 can propagatetowards central portion. The cracks from the chamfering line of theflexible display 100 may propagate into the bending area and the routingareas adjacent to the bending area. In some cases, cracks from thescribing lines at the inactive areas provided in a flat central portionof the flexible display 100 can propagate toward the active area anddamage various circuits in the inactive areas, such as the GIP.

Accordingly, selective areas along one or more scribing lines of theflexible display 100 may be substantially free of inorganic materiallayers. For example, area at one or more edges of the base layer 106 inthe flexible display 100, denoted as “the scribe line etch area” in FIG.13A, may be substantially free of insulation layers of inorganicmaterials such the buffer layer 126. In the scribe line etch areas, thebase layer 106 may be exposed or only a predetermined minimal thicknessof the buffer layer 126 may remain. Although the scribe line etch areasare marked at the top edge and the bottom edge of the flexible display100 in FIG. 13A, the location, the size and the shape of the scribe lineetch area are not particularly limited as shown in FIG. 13A. The scribeline etch area can be provided at the side edges of the flexible display100. In an embodiment in which the flexible display 100 is provided witha rounded base layer 106, the scribe line etch area may be provided atthe periphery of the active area.

Several side crack stopper structures may also be provided in the areabetween the edge (i.e., scribed line/chamfered line) and the active areain a central portion of the flexible display 100. For instance, arecessed channel can be formed in the inactive area by etching theinsulation layers. Also, a dummy wire trace pattern may be disposed inthe inactive area to change the direction of crack propagating from theouter edge of the flexible display 100 toward the circuits in theinactive area. Such crack stopper structures can be provided between acircuit (or other fragile elements) positioned in the inactive area andthe outer edge of the flexible display 100. For example, a metal tracehaving a strain reduction pattern and insulation layer covering themetal trace can be formed between the GIP and the edge of the flexibledisplay 100 as depicted in FIG. 9A (right side). While the recessedchannel and the dummy wire trace pattern are provided on the left andright sides, respectively, such crack stopper structures can be providedin the top and bottom sides as well.

It should be noted that the recessed channel on the left side of theactive area can also be provided on the right side of the active area.Likewise, the dummy wire trace with the strain-reducing pattern providedon the right side of the inactive area can also be provided on the leftside of the inactive area. In some embodiments, both the recessedchannel and the metal trace having the strain-reducing pattern can beprovided on one or more sides of the active area. In this configuration,the cracks propagating from the outer edge of the inactive area in thedirection towards the GIP may change its course due to the angle of thediamond metal/insulation trace formed before the GIP.

Patterning of insulation layers, especially the inorganic insulationlayers, can also be performed in the routing area between the activearea and the bend allowance section as well as the routing area betweenthe COF bonding area and the bend allowance section. Further, theinorganic material layers may be removed from at least some part ofareas adjacent to the chamfered lines so that cracks do not propagatefrom the chamfered line toward the conductive lines 120.

FIG. 13B is an enlarged view of lower left corner of the flexibledisplay near the notched area. In order to reduce crack initiation andpropagation from the inorganic layers near the chamfered line, theinsulation layer is etched in the area between the wire trace (e.g., VSSline) to the chamfered line. In particular, the buffer layer 126disposed on the base layer 106 in the area between the chamfered lineand the conductive line 120 in the bend allowance section, which isclosest to the chamfering line (e.g., VSS line) can be removed. In thisarea, the base layer 106 may be exposed or buffer layer 126 with alimited thickness (i.e., thinner than the buffer layer 126 under theconductive line 120) may remain. Accordingly, crack initiation andpropagation from the chamfered line can be hindered by the buffer layeretched area.

When etching the buffer layer 126 near the chamfering line, a stripe ofbuffer layer 126 can be configured to remain between the chamfered lineand the wire trace closest to the chamfered line as depicted in FIG.13B. This stripe of buffer layer can serve as a dam for inhibitingmoistures of other foreign material from reaching the wire trace fromthe chamfered side of the flexible display 100.

The aforementioned buffer layer etched area can also be applied in therouting area between the chamfering line and the closest wire trace. Thestripe of buffer layer 126 may also be provided in the routing area.Further, the buffer layer 126 under the conductive lines 120 and thepassivation layer 128 on the conductive lines 120 can be patterned tocorrespond to the trace of the conductive lines 120 throughout therouting area to further reduce the chance of crack propagation by theinorganic insulation layers in the routing areas next to the bendallowance section. For instance, the configuration of wire tracestructures depicted in FIGS. 11A and 11B may also be applied to the wiretraces in the routing areas.

FIG. 13C is an enlarged view near the notched area of the flexibledisplay 100, provided with another type of crack stopper structure. Inthis embodiment, an auxiliary conductive line 130 having the diamondtrace pattern is provided between the chamfered line and the wire trace(e.g., VSS). The buffer layer 126 under the auxiliary conductive line130 and the passivation 128 on the auxiliary conductive line 130 can beetched in the similar manner as depicted in FIGS. 11A and 11B.Accordingly, the auxiliary conductive line 130 may inhibit propagationof cracks from the chamfered line to the wire trace. The auxiliaryconductive line 130 may be a floating line. If desired, the auxiliaryconductive line 130 may extend outside the routing area towards thebottom edge of the flexible display 100. In some embodiments, theauxiliary conductive line 130 may be in contact with adjacent conductiveline 120. In addition to the auxiliary conductive line 130, the stripeof buffer layer 126 may also be provided to stop moisture or otherforeign materials traveling towards the auxiliary conductive line 130.

Micro-Coating Layer (MCL)

With the inorganic insulation layers etched away from the bend portionof the flexible display 100, the wire traces in the bend portion can bevulnerable to moistures and other foreign materials. In particular,various pads and conductive lines for testing the components duringmanufacturing of the flexible display 100 may be chamfered, and this canleave conductive lines extended to the notched edge of the flexibledisplay 100. Such conductive lines can easily corrode by the moistures,and cause other nearby conductive line to corrode as well.

Accordingly, a protective coating layer, which may be referred to as a“micro-coating layer” can be provided over the wire traces in the bendportion to provide added protection against moistures and other foreignmaterials. In addition to having a good moisture resistance, themicro-coating layer should have sufficient flexibility so that it can beused in the bend portion of the flexible display 100. Further, thematerial of the micro-coating layer may be a curable material with lowenergy within a limited time so that the components under themicro-coating layer are not damaged during the curing process.

FIG. 14A is a schematic illustration of one suitable exemplaryconfiguration of the micro-coating layer 132 in an embodiment offlexible display 100. The micro-coating layer 132 may be provided asphoto-curable (e.g., UV light, Visible light, UV LED) resin and coatedover the desired areas of the flexible display 100. In this regard, themicro-coating layer 132 is coated over the area between theencapsulation 114 and the COF 134 attached in the inactive area.Depending on the adhesive property of the micro-coating layer 132,however, the micro-coating layer 132 can be detached from theencapsulation 114 and/or the COF 134. Any open space between themicro-coating layer 132 and the encapsulation 114 or the COF 132 maybecome a defect site where moisture can permeate through.

Accordingly, the micro-coating layer 132 may be coated to overflow intoa part of the top surface of the encapsulation 114 for enhanced sealingbetween the encapsulation 114 and the micro-coating layer 132. Theadditional contact area between the micro-coating layer 132 and thesurface of the encapsulation 114 can provide stronger bonding, andreduce the cracks and corrosion of the wire traces at the bend portionof the flexible display 100. Likewise, the micro-coating layer 132 canbe coated on as least some part of the COF 134 for stronger bondingbetween the micro-coating layer 132 and the COF 134.

Referring to FIGS. 14B and 14C, the width of the encapsulation 114coated with the micro-coating layer 134 (denoted as Overflow_W1) and thewidth of the COF 134 coated with the micro-coating layer 134 (denoted asOverflow_W2) are not particularly limited and may vary depending on theadhesiveness of the micro-coating layer 132. As shown in FIG. 14B, theflexible display 100 may include a portion where the micro-coating layer132 on the encapsulation 114 is spaced apart from the sidewall of thepolarization layer 110. In some embodiments, the flexible display 100may include a portion where the micro-coating layer 132 on theencapsulation 114 is in contact with the polarization layer 110 disposedon the encapsulation 114 as depicted in FIG. 14C.

In one suitable configuration, the micro-coating layer 132 may be incontact with the polarization layer 110 at the two opposite corners(denoted “POL_CT”) while the micro-coating layer 132 only covers up tosome part of the encapsulation 114 in the areas between the two oppositecorners. After the bending process, the part of the flexible display 100where the micro-coating layer 132 is spaced apart from the polarizationlayer 110 may be configured as shown in FIG. 15A. In the region wheremicro-coating layer 132 is configured to be in contact with thepolarization layer 110, the flexible display 100 may be configured asshown in FIG. 15B.

It should be noted that the micro-coating layer 132 is dispensed in aresinous form, and may spread on the dispensed surface. The spreadingdynamic depends on the viscosity of the micro-coating layer 132 as wellas the surface energy of which the micro-coating layer 132 is dispensed.As such, the micro-coating layer 132 overflowed into the encapsulation114 may reach the polarization layer 110. When the micro-coating layer132 reaches the sidewall of the polarization layer 114, themicro-coating layer 132 may climb over the sidewall of the polarizationlayer 110. Such sidewall wetting of the micro-coating layer 132 can makeuneven edges over the surface of the polarization layer 132, which maycause various issues when placing another layer thereon. Accordingly,the amount of the micro-coating layer 134 dispensed on the targetedsurface can be adjusted to control the width of the micro-coating layer134 on the encapsulation layer 114.

The micro-coating layer 132 may be coated in a predetermined thicknessto adjust the neutral plane of the flexible display 100 at the bendportion. More specifically, added thickness at the bend portion of theflexible display 100 by the micro-coating layer 132 can change theneutral plane so that the plane of the wire traces is shifted closer tothe neutral plane.

In some embodiments, the thickness of the micro-coating layer 132 in thearea between the encapsulation 114 and the COF 134, which is measuredfrom the surface of the base layer 106, may be substantially the same asthe distance between the surface of the base layer 106 to the topsurface of the encapsulation 104. In such embodiments, the verticaldistance between the top surface of the micro-coating layer 132 in thebend allowance section and the top surface of the encapsulation 114 maybe less than 25 μm.

Various resin dispensing methods, such as slit coating, jetting and thelike, may be used to dispense the micro-coating layer 132 at thetargeted surface. In way of an example, the micro-coating layer 132 canbe dispensed by using a jetting valve. The dispensing speed from thejetting valve(s) may be adjusted during the coating process for accuratecontrol of the thickness and the spread size of the micro-coating layer132 at the targeted surface. Further, additional number of jettingvalues may be used to reduce the dispense time and limit the amount ofspread before the micro-coating layer 132 is cured through UVirradiation.

Divided VSS-VDD Wire Trace

Spreading dynamic of the micro-coating layer 132 over the wire tracescan be affected by the trace design of the wire traces. Morespecifically, patterning of the insulation layers along the wire tracein the bend portion of the flexible display 100 creates recessed areasand protruded areas, which essentially become a micro-grooved surface tobe covered by the micro-coating layer 132.

When applying the strain-reducing trace design in the wire traces,patterning of the insulation layers around the split sub-traces createsthe recessed open area, which is surrounded by the protruded stack ofwire traces. During coating of the micro-coating layer 132, some portionof the micro-coating layer droplet can permeate into the recessed openarea. It can hinder the spreading and reduce the maximum spreadingdiameter of the micro-coating layer 132 on such a micro-grooved surface,and result in some part of the bend portion being exposed without themicro-coating layer 132.

Decrease in the wettability of micro-coating layer 132 by thedistribution of the recessed areas and the protruded areas may bemagnified even more in the area over the wire trace applied with thegrid-like trace design shown in FIG. 9B. To counteract the viscid drag,in some embodiments, a wire trace, which includes multiple diamond-chaintraces adjoined side-by-side, can be provided with a rail between twoparts of the wire trace.

Referring to FIG. 16, a wire trace with a grid-like tracestrain-reducing trace design is provided with an elongated channelbetween divided grid-parts of the wire trace. Within the elongatedchannel, the conductive line 120 is not formed. Also, at least some ofthe inorganic insulation layers on the base layer 106 are removed in theelongated channel. The elongated channel between the grid-parts of thewire trace extends from the signal supplying side to the signalreceiving side of the wire trace. That is, the elongated channel may beextended in the direction parallel to the bending direction. It shouldbe noted that the separated parts of the wire trace on one side of theelongated channel is connected to the part of the wire trace on theopposite side of the elongated channel, and thus both parts of the wiretrace transmit the identical signal. The connection between the dividedparts of the wire trace may be achieved at one or both ends of the wiretrace by a conductive path, which may be a part of the wire trace. Theconnection of the divided parts of the wire trace may be achieved withinthe bend allowance section or outside the bend allowance section.

Even though the parts of the wire trace on each side of the elongatedchannel has the grid-like trace design, the reduced number ofdiamond-chain traces adjoined in each grid-part and the channel betweenthe grid-parts can reduce the viscid drag of the micro-coating layer132. More importantly, the elongated recessed channel between the partsof the wire trace serves as a path that improves the wettability of themicro-coating layer 132 over the wire trace. In sum, increase in themaximum spread diameter of the micro-coating layer 132 can be achievedby positioning one or more elongated channel within the wire having thegrid-like strain-reducing trace design.

It should be noted that the resistance of the wire trace can increasewith the elongated channel dividing the wire trace into multiplegrid-parts. Increase in the resistance of the wire can raise thetemperature of the wire trace when it is supplied with a signal.Accordingly, the number of elongated channels provided in a single wiretrace can depend on the signal transmitted via the wire trace. In somecases, the size of each diamond shaped link in a grid-like wire tracemay be larger than the size of diamond-shaped links in other wire tracesof the flexible display 100.

In one suitable configuration, one or more of power signal wires of theflexible display 100, such as the VDD and/or the VSS, has the grid-likewire trace formed of multiple diamond-chain traces adjoined side-by-sideas depicted in FIG. 16. The power signal wire trace includes one or moreelongated channels in its grid-like wire trace. Each of the elongatedchannels is provided between two divided grid parts, which are on theopposite sides of the elongated channel. The divided grid parts areconnected at one or both ends of the power signal wire. The size of thedivided grid parts may be substantially the same. That is, the number ofdiamond-chain traces forming a gird part on one side of the elongatedchannel may be the same as the number of diamond-chain traces forming agird part on the opposite side. If desired, however, the number ofdiamond-chain traces adjoined to each other to form one grid part maydiffer from the number of diamond-chain forming another grid part.

Although the concepts and teachings in the present disclosure aredescribed above with reference to OLED display technology, it should beunderstood that several features may be extensible to any form offlexible display technology, such as electrophoretic, liquid crystal,electrochromic, displays comprising discreet inorganic LED emitters onflexible substrates, electrofluidic, and electrokinetic displays, aswell as any other suitable form of display technology.

As described above, a flexible display 100 may include a plurality ofinnovations configured to allow bending of a portion or portions toreduce apparent border size and/or utilize the side surface of anassembled flexible display 100. In some embodiments, bending may beperformed only in the bend portion and/or the bend allowance sectionhaving only the conductive line 120 rather than active displaycomponents or peripheral circuits. In some embodiments, the base layer106 and/or other layers and substrates to be bent may be heated topromote bending without breakage, then cooled after the bending. In someembodiments, metals such as stainless steel with a passive dielectriclayer may be used as the base layer 106 rather than the polymermaterials discussed above. Optical markers may be used in severalidentification and aligning process steps to ensure appropriate bendsabsent breakage of sensitive components. Components of the flexibledisplay 100 may be actively monitored during device assembly and bendingoperations to monitor damage to components and interconnections.

Constituent materials of conductive line 120 and/or insulation layersmay be optimized to promote stretching and/or compressing rather thanbreaking within a bending area. Thickness of a conductive line 120 maybe varied across a bending area and/or the bend allowance section tominimize stresses about the bend portion or the bend allowance sectionof the flexible display 100. Trace design of conductive line 120 andinsulation layers may be angled away from the bending direction (i.e.,tangent vector of the curvature), meandering, waving, or otherwisearranged to reduce possibility of severance during bending. Thethickness of the conductive line 120, insulation layers and othercomponents may be altered or optimized in the bend portion of theflexible display 100 to reduce breakage during bending. Bend stressesmay be reduced by adding protective micro-coating layer(s) overcomponents in addition to disclosed encapsulation layers. Conductivefilms may be applied to the conductive line 120 before, during, or afterbending in a repair process. Furthermore, the constituent materialand/or the structure for conductive line 120 in a substantially flatarea of a flexible display 100 may differ from the conductive line 120in a bend portion and/or the bend allowance section.

These various aspects, embodiments, implementations or features of thedescribed embodiments can be used separately or in any combination. Theforegoing is merely illustrative of the principles of this invention andvarious modifications can be made by those skilled in the art withoutdeparting from the scope of the invention.

What is claimed is:
 1. A flexible display apparatus, comprising: aflexible base layer having an active area and an inactive area; a firstwire trace and a second wire trace on the flexible base layer, each ofthe first wire trace and the second wire trace having a buffer layer, apassivation layer and a conductive line between the buffer layer and thepassivation layer, at least a portion of the first wire trace and atleast a portion of the second wire trace are positioned in a bendallowance section of the flexible display apparatus at one of edges ofthe flexible display apparatus; and a sealing layer over at least theportion of the first wire trace and at least the portion of the secondwire trace positioned in the bend allowance section of the flexibledisplay apparatus, wherein the sealing layer has sufficient flexibilityand a moisture resistance.
 2. The flexible display apparatus of claim 1,wherein the first wire trace and the second wire trace are arranged in astaggered configuration.
 3. The flexible display apparatus of claim 2,wherein one of distended sections of the first wire trace is alignednext to an indented section of the second wire trace.
 4. The flexibledisplay apparatus of claim 1, wherein each of the first and second wiretraces have open space surrounded by portions of the conductive line. 5.The flexible display apparatus of claim 4, wherein the buffer layer andthe passivation layer is absent from the open space.
 6. The flexibledisplay apparatus of claim 1, wherein the passivation layer is patternedaccording to the conductive line.
 7. The flexible display apparatus ofclaim 6, wherein the passivation layer is absent from an area betweenthe first wire trace and the second wire trace.
 8. The flexible displayapparatus of claim 6, wherein the buffer layer is patterned according tothe conductive line.
 9. The flexible display apparatus of claim 8,wherein the buffer layer is etched away around the conductive line. 10.The flexible display apparatus of claim 1, wherein each of the first andsecond wire traces includes a reinforced portion at an end and a middleportion connected to the reinforced portion, the reinforced portionhaving a width wider than a width of the middle portion.
 11. Theflexible display apparatus of claim 10, wherein the middle portion ofeach of the first and second wire traces has open space surrounded byportions of the conductive line but the reinforced portion of each ofthe first and second wire traces does not include open space.
 12. Theflexible display apparatus of claim 10, wherein the reinforced portionis at an end of the bend allowance section.
 13. The flexible displayapparatus of claim 10, wherein each of the first and second wire tracesincludes another reinforced portion at another end, the other reinforcedportion having a width wider than a width of the middle portion.
 14. Theflexible display apparatus of claim 1, wherein the buffer layer and thepassivation layer include silicon oxide or silicon nitride.